The overall focus of this proposal is to delineate the molecular and genetic events which lead to the regulated expression of the neuroendocrine genes tyrosine hydroxylase (TH) and dopamine beta-hydroxylase. TH is the initial and rate limiting enzyme in the biosynthesis of dopamine, norepinephrine and epinephrine, and DBH catalyzes the conversion of dopamine to norepinephrine. TH and DBH are co-expressed in noradrenergic and adrenergic cells, and the expression of the TH and DBH genes are frequently coordinately regulated by environmental, neuronal and hormonal influences. This ongoing research program has identified several of the genetic regulatory elements which control the transcription of the TH and DBH genes, as well as the transcription factors which interact with the regulatory elements to control the rate of transcription. In this current proposal, we will utilize biochemical, molecular biology and cellular approaches to: (l) investigate how second messengers and protein kinase cascades interact with the tissue specific transcription factor Phox2a/Arix to influence transcription of the TH and DBH genes through analysis of Arix phosphorylation, (2) identify and characterize the proteins which repress DBH gene expression in inappropriate tissues, and (3) evaluate the interaction of transcription factors Phox2a/Arix, Phox2b/NBPhox, CREB/ATF and AP1 with the TH and DBH genes within intact cells. These experiments will define the mechanisms by which tissue specific transcription factors interact with ubiquitous factors to mediate selective expression of the TH and DBH genes. Knowledge of the mechanisms underlying the regulated expression of these genes is relevant to studies where dopaminergic cells are lost, such as Parkinson's disease, and where aberrant balance of neurotransmitters lead to disease, such as hypertension and bipolar mental disorders.